The invention relates to power roof ventilators and more particularly to a ventilator of the type comprising a centrifugal impellor driven by a motor about a vertical axis, and a housing encompassing the centrifugal impellor and the drive motor. The housing is so designed that it may be connected by means of hollow mount with the roof or a wall of a building premises to be power ventilated. The ventilator is so configured that at least in a part adjacent to a flat base member representing the connection with the mount, it has the outline of a rectangel or square and has an inlet port on a side adjacent to the mount and a radial outlet section with two outlet ports on opposite sides of the housing so that the air current is conducted away from the vicinity of the drive motor.
Such a roof ventilator has been proposed in the German patent application P No. 3,438,710, in which air is drawn in from a rood to be ventilated by a centrifugal impellor in which it moves axially before leaving it in a generally radial direction and passes through outlet ports. Since there are only two, opposite outlet ports, the air is swept away in a substantially sin-free, aligned flow clear of the ventilator and travels some distance clear of the ventilator in operation. This type of roof ventilator is furthermore characterized by a low power dissipation and by quiet running. However, experience has shown that inspection and servicing of such a roof ventilator is relatively involved and that the centrifugal impellor and the motor are not readily accessible from the outside for inspection.